When you have invited a new user and this user created his own Trial Subscription, then mostly this happens baause of a wrong login.
The background here is that your organization has configured AAD login for Signl4. But the user has used the standard Signl4 login putting in Username and Password manually instead of using the Microsoft button at the Signl4 login page.
To correct that you have to do the following steps:
- let the user login to his created Trial and let delete him his account:
- after that please re-invite this user and make sure that he is using the "Sign in with Microsoft" button